Starch consists of a mixture of amylose (15-30% w/w) and amylopectin (70-85% w/w). Amylose consists of linear chains of α-1,4-linked glucose units having a molecular weight (MW) from about 60,000 to about 800,000. Amylopectin is a branched polymer containing α-1,6 branch points every 24-30 glucose units; its MW may be as high as 100 million.
Sugars from starch, in the form of concentrated dextrose syrups, are currently produced by an enzyme catalyzed process involving: (1) liquefaction (or thinning) of solid starch with an α-amylase into dextrins having an average degree of polymerization of about 7-10; and (2) saccharification of the resulting liquefied starch (i.e. starch hydrolysate) with amyloglucosidase (also called glucoamylase or GA). The resulting syrup has a high glucose content. Much of the glucose syrup, which is commercially produced, is subsequently enzymatically isomerized to a dextrose/fructose mixture known as isosyrup.
Alpha-amylases (alpha-1,4-glucan-4-glucanohydrolases, E.C. 3.2.1.1) constitute a group of enzymes, which hydrolyze starch, glycogen, and related polysaccharides by cleaving internal α-1,4-glucosidic bonds at random. This enzyme class has a number of important commercial applications in, for example, starch liquefaction, textile desizing, starch modification in the paper and pulp industry, sweetener (e.g., sugar) manufacture and for brewing. These enzymes can also be used to remove starchy stains during dishwashing and laundry washing. Alpha-amylases are isolated from a wide variety of bacterial, fungal, plant and animal sources. Industrially, many important α-amylases are those isolated from Bacilli.
Amylases can be used commercially in the initial stages (liquefaction) of starch processing; in wet corn milling; in alcohol production; as cleaning agents in detergent matrices; in the textile industry for starch desizing; in baking applications as anti-staling agents; in the beverage industry; in oilfields in drilling processes; in deinking of recycled paper and in animal feed.
In recent years, attempts have been made to construct alpha-amylase variants having improved properties with respect to specific uses such as starch liquefaction, detergents and textile desizing.
There is a need in the industry for the identification and optimization of amylases, useful for various uses, including dishwashing and laundry washing processes. These second generation amylases will offer improved manufacturing and/or performance characteristics over the industry standard enzymes.
One characterized α-amylase is that of an alkaliphilic Bacillus sp. strain TS-23 which produces at least five kinds of enzymes exhibiting starch hydrolyzing activity. (Lin et al., 1998, “Production and properties of a raw-starch-degrading amylase from the thermophilic and alkaliphilic Bacillus sp. TS-23,” Biotechnol. Appl. Biochem. 28: 61-68).
However, there remains a need for a variant of an alpha-amylase, which variant in comparison to the corresponding parent alpha-amylase, i.e., unmutated alpha-amylase, has alpha-amylase activity and exhibits an alteration in at least one of the above mentioned properties relative to said parent alpha-amylase.